1. Field of the Invention
The present invention relates to a space photovoltaic power generation method and system for receiving sunlight in space so as to generate electric power, for transmitting the electric power to an electric power base via space by converting the electric power to a microwave, and for storing the electric power in the electric power base so as to allow the use of the electric power.
2. Description of the Prior Art
A solar cell is known as a small-size power generation system which utilizes sunlight. Furthermore, a photovoltaic power generation panel or the like, which can be set up on a building, is known as a power generation system intended for the home which utilizes sunlight. Such a photovoltaic power generation system built on the earth is not necessarily efficient fundamentally because of the attenuation of sunlight in the earth""s atmosphere and the alternation between shade and light caused by the alternation between day and night. A solar panel, which can be installed in a satellite, is known as a photovoltaic power generation device intended for space. Satellites can thus achieve missions by privately generating necessary electric power for observation and communications, etc. by using a solar panel. In either of the prior art power generation systems, specific equipment connected to the solar cell by cable is adapted to use the energy generated by the solar cell.
On the other hand, as the communication technology progresses according to results of recent space development works and the construction technology to construct a large-scale space structure progresses, research and development of a system that receives sunlight in space, generates electric power, and transmits the generated energy to a specific place such as a specific location on the earth or in space has been actively conducted. There can be provided an example of such a space photovoltaic power generation system including a plurality of power satellites arranged in space, each of which can focus sunlight to a number of solar panels, photoelectric-convert the incident sunlight so as to generate electric power, and then generate a microwave based on the generated energy and transmit the microwave to an electric power base built on the earth. Since each of the plurality of power satellites may generate a microwave having high energy, an array antenna that can distribute high power equipment, such as high-power amplifiers, among different locations can be effective as a transmission system. The electric power base built on the earth includes a receiving antenna for receiving incident microwaves. The electric power base converts the received microwaves into DC signals and then combine them into DC electric power.
In the above-mentioned prior art space photovoltaic power generation system, to ensure that the microwave transmitted from each of the plurality of geostationary power satellites is incident on the receiving antenna of the electric power base, the beamwidth of the microwave has to be narrowed. In the case of an array antenna, the area of the aperture has to be enlarged to narrow the beamwidth. This results in a disadvantage that the transmission antenna increases in size and hence each of the plurality of power satellites increases in size. On the other hand, to improve the power generation capability of the space photovoltaic power generation system constructed as above, a large number of power satellites each for transmitting a microwave towards the ground by a transmission antenna thereof should be arranged in space. In this case, it is assumed that the group of transmission antennas is a single huge phased array antenna for transmitting microwaves. A problem is that the area of the aperture of the array antenna defined as the group of transmission antennas is too large and the beamwidth of microwaves transmitted via the array antenna is therefore narrowed greatly, and this results in an increase in the per-unit-area electric power received on the earth.
The present invention is proposed to solve the above-mentioned problem. It is therefore an object of the present invention to provide a space photovoltaic power generation method capable of transmitting microwaves of high electric power generated from sunlight in space to an electric power base while making the beamwidth of the microwaves incident on an electric power base antenna match the size of the electric power base antenna, thereby preventing the per-unit-area electric power received by the electric power base antenna from becoming too large.
In accordance with an aspect of the present invention, there is provided a space photovoltaic power generation method of generating electrical energy from sunlight and converting the generated electrical energy into microwaves by means of a plurality of power satellites arranged in space, transmitting the microwaves to an electric power base, and generating electric power by means of the electric power base, the method comprising the steps of: dividing the plurality of power satellites into a plurality of groups each for including a number of power satellites; adjusting a plurality of microwaves transmitted from the plurality of power satellites included in each of the plurality of power satellite groups so that the plurality of microwaves are in phase with one another; and making a plurality of microwaves to be transmitted from each of the plurality of power satellite groups incoherent so that the plurality of microwaves do not interfere with other microwaves transmitted from any other one of the plurality of power satellite groups, and transmitting the plurality of incoherent microwaves to the electric power base.
In accordance with another aspect of the present invention, there is provided a space photovoltaic power generation system comprising: a plurality of power satellite groups each for including a number of power satellites each for generating electrical energy from sunlight in space, generating a microwave from the generated electrical energy, making the generated microwave incoherent so that the microwave does not interfere with other microwaves transmitted from any other one of the plurality of power satellite groups, and transmitting the incoherent microwave; a control unit for controlling the plurality of power satellites included in each of the plurality of power satellite groups so that a plurality of microwaves transmitted from the plurality of power satellites are in phase with one another; and an electric power base located at a remote site for receiving the plurality of microwaves transmitted from the plurality of power satellites included in each of the plurality of power satellite groups, and for generating electric power from the plurality of microwaves received.
In accordance with a preferred embodiment of the present invention, the control unit includes a location measurement unit for measuring a location of each of the plurality of power satellites included in each of the plurality of power satellite groups, a phase adjustment amount calculation unit for calculating an amount of phase adjustment to be made to the microwave which each of the plurality of power satellites included in each of the plurality of power satellite groups will transmit from the measured location, and a phase control unit for adjusting a phase of the microwave which each of the plurality of power satellites included in each of the plurality of power satellite groups will transmit according to the amount of phase adjustment calculated by the phase adjustment amount calculation unit so that the plurality of microwaves transmitted from the plurality of power satellites included in each of the plurality of power satellite groups are in phase with one another.
The space photovoltaic power generation system can comprise a plurality of control satellites that serve as the control unit, the plurality of control satellites being associated with the plurality of power satellite groups, respectively.
As an alternative, space photovoltaic power generation system can comprise a plurality of control satellites associated with the plurality of power satellite groups, respectively, each of the plurality of control satellites including the location measurement unit, and a transmission unit for informing each of the plurality of power satellites included in each of the plurality of power satellite group of data on the location of each of the plurality of power satellites measured by the location measurement unit. In addition, each of the plurality of power satellites included in each of the plurality of power satellite group can include the phase adjustment amount calculation unit and the phase control unit, and adjusts the phase of the microwave which each of the plurality of power satellites will transmit so that the microwave is in phase with any other microwave transmitted from any other one of the plurality of power satellites according to the calculated amount of phase adjustment.